(1) Field of the Invention
The present invention relates to an image processing device for correcting the characteristics of a display panel by performing processes for an inputted image signal so as to display the processed image signal as a visually satisfactory image in portable display apparatuses such as a notebook personal computer, a PDA and the like.
(2) Description of the Related Art
With the improvement in the performance of personal computers (to be referred to as “PC(s)” hereinafter), an increased number of image signals have been handled in recent years by PCs via digital video/versatile discs (to be referred to as “DVD(s)” hereinafter), networks and the like. Such a trend applies not only to desktop PCs but also to portable notebook PCs. Furthermore, some personal digital assistants (to be referred to as “PDA(s)” hereinafter) which are smaller in size than notebook PCs also handle image signals in these days.
However, since PCs are not originally intended for handling image signals, there is a fact that they are inferior to image display apparatuses including television, in terms of the image quality that they can offer. Images that notebook PCs can provide, in particular, lack brightness, colorfulness, and vividness due to reasons stemming from power consumption constraints including that of (i) the backlight of a liquid crystal panel which is used as a display device, not being able to be brightened much and (ii) the color filter not being able to be darkened as required because brightness needs to be ensured by saving power consumption.
Meanwhile, image display apparatuses such as the TV handle image signals in compliance with standards including NTSC. Digital image signals reproduced by a DVD and the like are also compliant with such standards as ITU-R (International Telecommunication Union, Radio Communication Sector) 656. However, while handling image signals of DVDs and others compliant with some standards or others, PCs often handle image signals such as graphic images, images acquired by a digital camera and a capture card and others which are not necessarily in conformity with standards. Accordingly, both types of image signals are directly displayed on the same liquid crystal panel, indicating that satisfactory display images are not obtained from each type of the image signals.
Under these circumstances, a satisfactory image quality for display is generally obtained by an image processing device that processes an input image signal and outputs the processed signal to a liquid crystal panel. In so doing, existing image processing devices acquire an image signal such as an RGB signal and a YIQ signal, and perform processes such as color correction and gamma correction for the image signal so as to carry out optical correction for a video camera as well as nonlinearity correction for a display device and the like.
As an example of such image processing devices, there exists an image processing device that (i) detects the amount of noise, white peak, black peak and the average brightness from an input image signal, (ii) controls a lowpass filter, a contour control circuit, a video chroma circuit, and a gamma correction circuit on the basis of the result of such detection, and (iii) performs image processing for the inputted image signal (Refer to Japanese Laid-Open Patent Application No. H6-169437 as an example).
However, these above-mentioned image processing devices require many pieces of hardware in order to calculate white peak, black peak, and the average brightness. Therefore, it is difficult for these image processing devices to be employed by portable apparatuses including notebook PCs in terms of power consumption and the scale of circuits to be mounted. Furthermore, since a uniform processing is performed for an image signal without taking into account the characteristics of a display device, there is a problem that image quality of a sufficient level cannot be obtained.
Moreover, while PCs are capable of a multi-window display of an image signal compliant with such a standard as NTSC as well as a unique image signal which does not abide by any standard, they cannot offer satisfactory display images from each of the above image signals.
The present invention has been conceived in view of the aforementioned problems, and it is an object of this invention to provide an image processing device that (i) is suited to be incorporated into a portable display device such as a notebook PC in terms of power consumption and the scale of circuits to be mounted, (ii) is capable of vividly displaying the mixture of image signals, including signals that are compliant with such a standard as NTSC and do not comply to any standards, and (iii) allows, even when more than one kind of display devices are used, such display devices to be performed of optimal brightness/color correction and enhancement as well as allowing volume production of display apparatuses which incorporate one of such display devices and an image processing device as a set.